Last month I spent four days in the town of Egmont, BC. My husband and I had joined a friend on his annual excursion to the stomping grounds of his youth. We trailered the friend’s boat, Scherzo, up through Oregon and Washington and into British Columbia. We took a ferry and then ditched the car in Sechelt, piled our belongings and food into Scherzo, and headed up the Sechelt Inlet to arrive in Egmont. Incidentally, Egmont is entirely reachable by road, but it was kind of cool showing up in a little boat to the dock of the house we had rented.
© Allison J. Gong
2024-08-15
On our way up Sechelt Inlet I had noticed quite a bit of brown scum on the surface of the water. I couldn’t collect any on my hands and it didn’t have a detectable odor, but some of my cerebral neurons did their job and the name Noctiluca came into my head. Noctiluca scintillans is a bioluminescent dinoflagellate. It is a regular component of the plankton in Monterey Bay at this time of year. What makes it distinct from other dinoflagellates are its large size (can be greater than 1mm in diameter) and the fact that its hydrophobic theca (cell wall) causes cells to get stuck at the surface of the water. They can look like tiny bubbles floating at the surface.
There wasn’t as much Noctiluca at our dock in Egmont as we’d seen on our way up the inlet, but it was worth going out at night just to see. Dinoflagellates and other bioluminescent critters light up when disturbed. We borrowed Scherzo‘s oar to disturb the water and see what happened. We could see light when Alex drew the oar back and forth in the water, but a washing machine-like agitation was the best for getting the cells to flash.
Bioluminescence is one of those phenomena that never gets tiring. In this case, each Noctiluca cell emits one tiny flash of light when it gets bumped. These photos give you an idea of how dense the population was. Dinoflagellates tend to be late-season bloomers, becoming more abundant than the diatoms that dominate the spring and early summer phytoplankton. Many dinoflagellates, despite being considered part of the phytoplankton, are heterotrophic either in addition to or instead of being autotrophic (photosynthetic). Noctiluca is one of the heterotrophic dinoflagellates. It preys on smaller cells, including diatoms, small invertebrate larvae, and fish eggs.
If I had been at home with my lab supplies at hand I would have collected some of the cells in a scintillation vial, brought them into a dark room in the house, and shaken them up to observe the bioluminescence under controlled conditions. As it was, seeing it in the field, so to speak, was really cool.